The present invention resides in an improved double block and vent valve system wherein means are provided in the double block and vent assembly portion of the valve such that the fluid passing through the valve, and in particular through the assembly, does so without irs flow stream being substantially impeded by the configuration of the assembly.
In double block and vent valve systems, such as disclosed in aforementioned U.S. Patent No. 4,798,223, valves using cages in which upper and lower plugs coact against annularly extending inwardly directed shoulders are known. This arrangement is often quite acceptable and effective for sealing the valve against fluid leaching when the plugs are in a closed to flow condition. Such valves have found successful application in power plants wherein the double block and vent feature insures safe and controlled delivery of combustible fluids to the burners. In such applications, the valves are made very large to accommodate the high volume of fluid needed to produced a desired burn. This makes any disruption in the flow path followed by the fluid through the valve less pronounced given the size of the obstruction taken relative to volume of fluid affected. However, in applications of the double block and vent valve system wherein the size of the valve and the volume of fluid passing through it is not as disproportionately large taken relative to any flow path obstruction that may exist, such as in the case of a valve which feeds fuel to the ignitor of a combustion chamber, the fluid flow path through the double block and vent assembly may experience heightened resistance to flow.
Additionally, in fuel burning systems of the type in which the present invention may be involved, safety standards set by code require the valve to contain seals preventing leaking of the fluid through moving or operational parts thereof. This requirement is important in power plant systems wherein the fluid is ignitable and must not communicate with electrical components of the valve thereby causing possible inadvertent ignition of the escaping pressurized fluid in the case where a seal fails or is partially failing. To this end, it is desirable to construct a valve such that any failure occurring at a seal interface is protected by a redundancy in the system such that the flammable fluid is vented exteriorly of the valve in a safe manner. Also, it is desirable to vent such leaching pressurized fluid or gas to atmosphere at a location remotely of the actuator component parts.
Notwithstanding, previously known double block and vent valve systems employ actuator means which are integrally formed with the valve housing. Often one of many different types of actuators may be called by specification to be used thereby presenting a need to form a valve capable of being generically mated with different types of actuators. In so doing, it is thus necessary to construct the valve as a self-contained apparatus sealed independently of its actuator and capable of being connected to any one of a number of different actuator types without fluid leaching from it.
Accordingly, it is an object of the present invention to provide a double block and vent valve system wherein the block and vent assembly does not substantially impede the path followed by fluid flowing through the valve.
It is a further object of the present invention to provide a valve of the aforementioned type wherein means are provided for producing a redundancy in the valve against leaching of fluid through seal interfaces existing between mechanically moving parts.
Still a further object of the present invention is to provide a valve of the aforementioned type being so constructed as to be self-contained relative to the actuator which articulates it between open and closed positions such that it can be generically mounted to any one of a variety of different type actuators.
It is still a further object of the present invention to provide a double block and vent valve system so constructed as to be capable of venting flammable fluids to atmosphere through a means provided in the valve for directing such escaping fluids away from the actuator which articulates it.